tonight, general david petraeus steps down after admitting to having an affair. petraeus called his behavior unacceptable as the leader of the spy agency. cbs reporter tara mergener in washington where the resignation has shocked the intelligence community as well as top political leaders. tara. >> reporter: indeed. good evening, allen. yes, petraeus' resignation absolutely came as a shock here in washington ending the long career of a well respected and very high-profile public servant. cia director david petraeus submitted a letter of resignation to president obama admitting he had an extramarital affair. the president accepted his resignation. petraeus who has been married for 37 years says he showed, quote, extremely poor judgment when he had the affair. petraeus has been running the cia since september of 2011. before that, he was in charge of allied forces in afghanistan. and he also oversaw coalition forces in iraq. in a letter to cia employees, petraeus wrote, such behavior is unacceptable both as a husband and as the leader of an organization such as our